1. Technical Field
The present invention relates generally to a class of derivatives of 6,7-dihydro-5H-imidazo[1,2-a]imidazole-3-sulfonic acid, the synthesis of these compounds, their use in the treatment of inflammatory disease, and pharmaceutical compositions comprising these compounds.
2. Background Information
Research spanning the last decade has helped to elucidate the molecular events attending cell-cell interactions in the body, especially those events involved in the movement and activation of cells in the immune system. See generally, Springer, T. Nature, 1990, 346, 425-434. Cell surface proteins, and especially the Cellular Adhesion Molecules (“CAMs”) and “Leukointegrins”, including LFA-1, MAC-1 and p150,95 (referred to in WHO nomenclature as CD18/CD11a, CD18/CD11b, and CD18/CD11c, respectively) have correspondingly been the subject of pharmaceutical research and development having as its goal the intervention in the processes of leukocyte extravasation to sites of injury and leukocyte movement to distinct targets. For example, it is presently believed that prior to the leukocyte extravasation, which is a mandatory component of the inflammatory response, activation of integrins constitutively expressed on leukocytes occurs and is followed by a tight ligand/receptor interaction between integrins (e.g., LFA-1) and one or several distinct intercellular adhesion molecules (ICAMs) designated ICAM-1, ICAM-2, ICAM-3 or ICAM-4 which are expressed on blood vessel endothelial cell surfaces and on other leukocytes. The interaction of the CAMs with the Leukointegrins is a vital step in the normal functioning of the immune system. Immune processes such as antigen presentation, T-cell mediated cytotoxicity and leukocyte extravasation all require cellular adhesion mediated by ICAMs interacting with the Leukointegrins. See generally Kishimoto, T. K.; Rothlein; R. R. Adv. Pharmacol. 1994, 25, 117-138 and Diamond, M.; Springer, T. Current Biology, 1994, 4, 506-517.
A group of individuals has been identified which lack the appropriate expression of Leukointegrins, a condition termed “Leukocyte Adhesion Deficiency” (Anderson, D. C.; et al., Fed. Proc. 1985, 44, 2671-2677 and Anderson, D. C.; et al., J. Infect. Dis. 1985, 152, 668-689). These individuals are unable to mount a normal inflammatory and/or immune response(s) due to an inability of their cells to adhere to cellular substrates. These data show that immune reactions are mitigated when lymphocytes are unable to adhere in a normal fashion due to the lack of functional adhesion molecules of the CD18 family. By virtue of the fact that LAD patients who lack CD18 cannot mount an inflammatory response, it is believed that antagonism of CD18, CD11/ICAM interactions will also inhibit an inflammatory response.
It has been demonstrated that the antagonism of the interaction between the CAMs and the Leukointegrins can be realized by agents directed against either component. Specifically, blocking of the CAMs, such as for example ICAM-1, or the Leukointegrins, such as for example LFA-1, by antibodies directed against either or both of these molecules effectively inhibits inflammatory responses. In vitro models of inflammation and immune response inhibited by antibodies to CAMs or Leukointegrins include antigen or mitogen-induced lymphocyte proliferation, homotypic aggregation of lymphocytes, T-cell mediated cytolysis and antigen-specific induced tolerance. The relevance of the in vitro studies are supported by in vivo studies with antibodies directed against ICAM-1 or LFA-1. For example, antibodies directed against LFA-1 can prevent thyroid graft rejection and prolong heart allograft survival in mice (Gorski, A.; Immunology Today, 1994, 15, 251-255). Of greater significance, antibodies directed against ICAM-1 have shown efficacy in vivo as anti-inflammatory agents in human diseases such as renal allograft rejection and rheumatoid arthritis (Rothlein, R. R.; Scharschmidt, L., in: Adhesion Molecules, Wegner, C. D., Ed., 1994, 1-8; Cosimi, C. B., et al., J. Immunol. 1990, 144, 4604-4612 and Kavanaugh, A. et al., Arthritis Rheum. 1994, 37, 992-1004) and antibodies directed against LFA-1 have demonstrated immunosuppressive effects in bone marrow transplantation and in the prevention of early rejection of renal allografts (Fischer, A.; et al., Lancet, 1989, 2, 1058-1060 and Le Mauff, B.; et al., Transplantation, 1991, 52, 291-295).
It has also been demonstrated that a recombinant soluble form of ICAM-1 can act as an inhibitor of the ICAM-1 interaction with LFA-1. Soluble ICAM-1 acts as a direct antagonist of CD18,CD11/ICAM-1 interactions on cells and shows inhibitory activity in in vitro models of immune response such as the human mixed lymphocyte response, cytotoxic T cell responses and T cell proliferation from diabetic patients in response to islet cells (Becker, J. C.; et al., J. Immunol. 1993, 151, 7224 and Roep, B. O.; et al., Lancet, 1994, 343, 1590).
Thus, the prior art has demonstrated that large protein molecules which antagonize the binding of the CAMs to the Leukointegrins have therapeutic potential in mitigating inflammatory and immunological responses often associated with the pathogenesis of many autoimmune or inflammatory diseases. However proteins have significant deficiencies as therapeutic agents, including the inability to be delivered orally and potential immunoreactivity which limits the utility of theses molecules for chronic administration. Furthermore, protein-based therapeutics are generally expensive to produce.
It follows that small molecules having the similar ability as large protein molecules to directly and selectively antagonize the binding of the CAMs to the Leukointegrins would make preferable therapeutic agents.
Several small molecules have been described in the literature that affect the interaction of CAMs and Leukointegrins. For example, U.S. Pat. No. 6,355,664 and the corresponding WO 98/39303 disclose a class of small molecule, having a hydantoin core, that are inhibitors of the interaction of LFA-1 and ICAM-1. Of greater relevance to the present invention is U.S. Pat. No. 6,492,408, which discloses compounds that instead have an 6,7-dihydro-5H-imidazo[1,2-a]imidazole core. While the compounds that are specifically described by U.S. Pat. No. 6,492,408 have a more potent inhibitory affect upon the interaction of CAMs and Leukointegrins than do the hydantoins of U.S. Pat. No. 6,355,664 and the corresponding WO9839303, they nevertheless are not ideal therapeutic agents because the rate at which they are metabolized is undesirably high. Additional inhibitors of the interaction of LFA-1 and ICAM-1 having the 6,7-dihydro-5H-imidazo[1,2-a]imidazole core structure are described in U.S. Pat. Nos. 6,844,360 and 6,852,748.
The problem to be solved by the present invention is to find additional small molecules that have good inhibitory effect upon the interaction of CAMs and Leukointegrins, while also having an acceptable metabolic profile.